There is some risk associated with buying anything, whether old or new.

I would argue that it can be even riskier buying modern, firmware-driven, plastic, made-in-China equipment that will likely fail within 5 years and at that point be completely unrepairable.

As long as you mitigate your risk, buying older hi-fi gear should not be any riskier than buying new equipment. It can be less risky to buy well-cared-for older gear than newer stuff in terms of long-term reliability. Now, do the manufacturers or stores want you to know that..? Of course not.

Much of the equipment I work on was made in the ’70s and ’80s and hasn’t failed catastrophically. Yes, it might need cleaning, service and adjustment, but everything does eventually. A lot of newer gear (Cambridge, Marantz, NAD etc) fails after such a short time that it’s embarrassing, for everyone.

You need to know what you are looking for and how to test older gear of course. This will involve listening to it and operating it. Beyond that, an inspection either pre or post-purchase is a very sensible idea and can potentially save a lot of money.

There are, unfortunately, people knowingly selling faulty gear, especially on GumTree. Be very careful and if in doubt, seek advice.